Zoom lens system

ABSTRACT

A zoom lens system of a relatively high zoom ratio about 2.5 to 3.5 ranging to a wide field angle such as 76 degrees is disclosed. The zoom lens system comprises, from the object to the image side, a first movable negative lens group, a second movable positive lens group, a third stationary negative lens group and a fourth movable positive lens group with a first to third variable air spaces formed therebetween, respectively. And, the zoom lens system functions as an inverted telephoto type lens system in the shorter focal length range of the whole lens system by means of a combination of only the first lens group as a front negative group and the whole of the second to fourth lens groups as a rear positive group, while the zoom lens system functions as a telephoto type lens system in the longer focal length range of the whole lens system by means of a combination of the whole of the first and second lens groups as a front positive group and the whole of the third and fourth lens groups as a rear negative group.

This is a division of application Ser. No. 842,661, filed on May 15,1986 (issued as U.S. Pat. No. 4,759,617), which is a continuation ofSer. No. 445,528, filed on Nov. 30, 1982 (issued as U.S. Pat. No.4,591,235 on May 27, 1986).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a zoom lens system of a high zoom ratioabout 3 ranging from a telephoto to a considerably wide field angle foruse in a still camera, such as 35 mm SLR cameras.

2. Description of the Prior Art

In this field of art, there has been various attempts to provide a zoomlens system of relatively high zoom ratio ranging to wide field angle.Prior art zoom lens systems provided through such attempts can beroughly classified into two types, the first one having a negative frontlens group, while the second one having a positive front lens group.

The first type is in its nature favorable to the purpose of providingthe wide angle zoom lens system ranging to a considerably wide fieldangle, while it is unfavorable to the reduced total length and thecompactness of the lens system. A most popular and simplified zoom lenssystem classified into the first type is a so-called two-group zoom lenssystem consisting of a negative front lens group and a positive rearlens group. Although such a two-group zoom lens system is suitable for alimited zoom ratio, such as 2, it is difficult to further increase thezoom ratio.

On the other hand, in the second type of zoom lens system with the frontpositive lens group, if the zoom range is tried to reach a focal lengthless than the length of diagonal line of the effective image plane, thefocusing by means of moving the front positive lens group is difficultor the diameter of the front positive lens group is excessivelyincreased. A typical example of zoom lens system classified into thesecond type is a so-called four-group zoom lens system consisting of afront focusing lens group movable for focusing but left stationary uponzooming, a variator lens group movable for zooming, a compensator lensgroup movable for zooming and a stationary relay lens group. In such afour-group zoom lens system, if the zoom range is tried to extend to afocal length less than 40 mm with the focusing capability by means ofthe front lens group and the compactness of the whole lens systemmaintained, the focal lengths of the front lens group and the variatorlens group become excessively short to cause various aberrations whichare difficult to be sufficiently corrected.

An example of a zoom lens system of a high zoom ratio ranging from atelephoto to wide field angle is disclosed in Japanese PatentPublication No. 55-14403. A co-pending U.S. Patent Application Ser. No.393,492 (issued as U.S. Pat. No. 4,516,839) is another example of such azoom lens system.

The prior art is still seeking to provide a relatively compact andeconomical zoom lens system having a relatively high zoom ratio rangingto the wide angle range with adequate optical correction.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a zoom lens system witha relatively high zoom ratio about 2.5 to 3.5 ranging to a wide fieldangle about 76 degrees while maintaining a compact size.

Another object of the present invention is to provide a zoom lens systemwith aberrations well corrected across the entire zoom range.

According to the present invention, the zoom lens system comprises, fromthe object to the image side, a first movable negative lens group, asecond movable positive lens group, a third stationary negative lensgroup and a fourth movable positive lens group with a first to thirdvariable air spaces formed therebetween, respectively. And, the zoomlens system functions as an inverted telephoto type lens system in theshorter focal length range of the whole lens system by means of acombination of only the first lens group as a front negative group andthe whole of the second to fourth lens groups as a rear positive group,while the zoom lens system functions as a telephoto type lens system inthe longer focal length range of the whole lens system by means of acombination of the whole of the first and second lens groups as a frontpositive group and the whole of the third and fourth lens groups as arear negative group. By this feature, the total length of thew hole lenssystem at the longer focal length side is reduced in comparison with theconventional two-group zoom lens ssytem. The above functions areachieved by reducing the first and third variable air spaces andincreasing the second variable air space in accordance with the increaseof the focal length of the whole lens system by means of axial movementsof the first, second and fourth lens groups with the third lens groupleft stationary during zooming. The present invention is furthercharacterized by the first lens group including a negative lens at itsobject side end. This feature is greatly effective to the desiredcompactness of the lens system.

According to another feature of the present invention, the lens systemfulfills the following condition:

    0.5<R/|f.sub.1 |<1.3

wherein, R represents a radius of curvature of the object side one of apair of refractive surface defining the first air space numbered fromthe object side in the first lens group, and f₁ represents the focallength of the first lens group.

The features of the present invention which are believed to be novel areset forth with particularity in the appended claims. The presentinvention, both as to its organization and manner of operatior, togetherwith further objects and advantages thereof, may best be understood byreference to the following description, taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents a schematic view for showing the lens group movementsin the lens system according to the present invention between theshortest and longest focal lengths;

FIG. 2 represents a cross sectional view of the lens system according toa first embodiment of the present invention for the shortest focallength;

FIG. 3 represents a cross sectional view of the lens system according toa second embodiment of the present invention for the shortest focallength;

FIG. 4 represents a cross sectional view of the lens system according toa third embodiment of the present invention for the shortest focallength;

FIG. 5 represents a cross sectional view of the lens system according toa fourth embodiment of the present invention for the shortest focallength;

FIG. 6 represents a cross sectional view of the lens system according toa fifth embodiment of the present invention for the shortest focallength;

FIG. 7 represents a cross sectional view of the lens system according toa sixth embodiment of the present invention for the shortest forcallength;

FIGS. 8a to 8c represent the aberration curves of the first embodimentfor the longest focal length;

FIGS. 9a to 9c represent the aberration curves of the first embodimentfor a medium focal length;

FIGS. 10a to 10c represent the aberration curves of the first embodimentfor the shortest focal length;

FIGS. 11a to 11c represent the aberration curves of the secondembodiment for the longest focal length;

FIGS. 12a to 12c represent the aberration curves of the secondembodiment for a medium focal length;

FIGS. 13a to 13c represent the aberration curves of the secondembodiment for the shortest focal length;

FIGS. 14a to 14c represent the aberration curves of the third embodimentfor the longest focal length;

FIGS. 15a to 15c represent the aberration curves of the third embodimentfor a medium focal length;

FIGS. 16a to 16c represent the aberration curves of the third embodimentfor the shortest focal length;

FIGS. 17a to 17c represent the aberration curves of the fourthembodiment for the longest focal length;

FIGS. 18a to 18c represent the aberration curves of the fourthembodiment for a medium focal length;

FIGS. 19a to 19c represent the aberration curves of the fourthembodiment for the shortest focal length;

FIGS. 20a to 20c represent the aberration curves of the fifth embodimentfor the longest focal length;

FIGS. 21a to 21c represent the aberration curves of the fifth embodimentfor the shortest focal length;

FIGS. 22a to 22c represent the aberration curves of the fifth embodimentfor the shortest focal length;

FIGS. 23a to 23c represent the aberration curves of the sixth embodimentfor the longest focal length;

FIGS. 24a to 24c represent the aberration curves of the sixth embodimentfor a medium focal length; and

FIGS. 25a to 25c represent the aberration curves of the sixth embodimentfor the shortest focal length.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description is provided to enable any person skilled inthe optical and camera field to make and use the invention and setsforth the best modes contemplated by the inventor for carrying-out hisinvention. Various modifications, however, will remain readily apparentto those skilled in the art, since the generic principles of the presentinvention have been defined herein specifically to provide a relativelyeconomical and easily manufactured compact zoom lens system. Thederivation of the formulas and the relation of the powers set forthherein can be accomplished with the assistance of a computer. Thepresent invention represents the parameters of a compromise balance ofacceptable aberrations which can be relatively easily manufactured toprovide a low cost lens system for utilization with a 35 mm SLR camera.

In the drawings, schematic cross sectional views disclose the positionof the lens groups and lens elements for the shortest focal length witharrows below the lens groups representing the directions of theirmovements for zooming toward the longest focal length. Due to the numberof lens elements involved, it was not deemed appropriate to includeindividual designation of the radii of curvature and axial distances foreach lens element and air space. These values, however, are provided inthe accompanying tables set forth herein, and the schematic crosssectional views of the respective embodiments follow the normalconventions of an object at the left-hand side of the drawing and theimage plane at the right-hand side.

As disclosed in FIGS. 1 to 7, the present invention provides a zoom lenssystem of a relatively high zoom ratio ranging to a considerably widefield angel, comprising a first lens group (L₁) of a negative refractivepower including a negative lens at its object side end, a second lensgroup (L₂) of a positive refractive power located on the image side ofthe first lens group (L₁) with a first variable air space (l₁), a thirdlens group (L₃) of a negative refractive power located on the image sideof the second lens group (L₂) with a second variable air space (l₂), anda fourth lens group (L₄) of a positive refractive power located on theimage side of the third lens group (L₃) with a third variable air space(l₃), wherein the first and third variable air spaces (l₁ and l₃) arereduced and the second variable air space (l₂) is increased inaccordance with the increase of the focal length of the whole lenssystem by means of the axial movements of the first, second and fourthlens groups(L₁, L₂ and L₄) with the third lens group (L₃) leftstationary during the zooming.

The lens system according to the present invention fulfills thefollowing condition:

    0.5<R/|f.sub.1 |<1.3                     (1)

wherein, R represents a radius of curvature of the object side one of apair of refractive surfaces defining the first air space numbered fromthe object side in the first lens group (L₁), and f₁ represents thefocal length of the first lens group (L₁).

As is understood from the above description, the present invention ischaracterized by the front negative lens in the first lens group (L₁).In the zoom lens system of a high zoom ratio, the increased diameter ofthe first lens group is generally a problem to be solved. The first lensgroup (L₁) with such a front negative lens in accordance with thepresent invention is remarkably effective to reduce the diameter offirst lens group in comparison with a first lens group having a positivelens at the object side end thereof. This makes the whole lens systemcompact. The front negative lens in the first lens group of the presentinvention can be a doublet if necessary.

Further, in accordance with the present invention, the third lens group(L₃) is left stationary upon zooming. This feature effectivelysimplifies the lens barrel mechanism since the number of zoom cams forcontrolling the lens groups movements is reduced. In a zoom systemhaving four lens groups as in the present invention, it is generallyrecommended to locate the diaphragm aperture stop(s) at the third lensgroup (L₃). In this circumstance, the feature of the present inventionthat the third lens group(L₃) is stationary renders the diaphragmaperture stop(s) also stationary with respect to the direction along theoptical axis. This simplifies a mechanism necessary to adjust thediaphragm aperture stop(s).

The above mentioned condition(1) relates to the radius of curvature ofthe object side one of a pair of refractive surfaces defining the firstair space numbered from the object side, i.e. the image side surface ofthe negative lens located at the object side end of the first lensgroup(L₁). If the lower limit of condition(1) is violated, coma would begreatly generated in the zonal to marginal area upon zooming in themedium to longest focal length, such coma being difficult to besufficiently corrected. On the contrary, if the upper limit ofcondition(1) is violated, it would be difficult to balance thecorrection of the spherical aberration with the deterioration of thecorrection for coma and distortion avoided.

FIG. 1 is for explaining the lens group movements of the lens systemaccording to the present invention in more detail, in which the solidlines between the shortest focal length arrangement(s) and the longestfocal length arrangement (L) respectively represent the movements of thefirst lens group(L₁), the second lens group(L₂) and the fourth lensgroup(L₄), while the broken line represents that the third lensgroup(L₃) is left stationary upon zooming. Referring to FIG. 1, the lenssystem fulfills the following conditions:

l₁ >l₁ '

l₂ <l₂ '

l₃ >l₃ '

wherein l₁, l₂ and l₃ represent the first to third variable air spacesfor the shortest focal length (S), respectively, while l₁ ', l₂ ' and l₃' represent the first to third variable air spaces for the longest focallength (L), respectively. The condition, l₁ >l₁ ' is necessary forrealizing an inverted telephoto type in the shorter focal length side(S), while the condition, l₂ >l₂ ' for realizing a telephoto type in thelonger focal length side (L). For the purpose of realizing a telephototype in the longer focal length arrangement (L), it is further necessaryto make the total focal length of the first and second lens groupspositive, and the total focal length of the third and fourth lens groupsnegative. This is summarized by the following conditions:

    f.sub.2 <|f.sub.1 |                      (2)

    |f.sub.3 |<f.sub.4                       (3)

wherein f₁, f₂, f₃ and f₄ represent the focal lengths of the first tofourth lens groups, respectively.

According to the present invention it is further recommended to fulfillthe following conditions:

    0.9<f.sub.2 /f.sub.w <1.5                                  (4)

    0.8<|f.sub.3 |/f.sub.w >1.6              (5)

    0.5<|f.sub.1 |/√f.sub.w ·f.sub.t <1.2 (6)

wherein, f_(w) and f_(t) represent the shortest and longest focallengths of the whole lens system, respectively.

Conditions (4) and (5) are both for achieving a desired aberrationcorrection all over the entire zoom range with the movement of the thirdlens group (L₃) avoided. If the lower limit of conditions (4) isviolated, the refractive power of the second lens group (L₂) would beexcessively increased, which makes it difficult to correct the sphericalaberration and astigmatism although the excessive refractive power ofthe second lens group (L₂) may be rather favorable to the compactness ofthe system. To correct such spherical aberration and astigmatism, itwould be inevitable to move the third lens group (L₃). On the contrary,if the upper limit of condition (4) is violated, the refractive power ofthe second lens group (L₂) would be excessively decreased to make thelens system bulky both in its total length and diameter, although theaberration correction would be easy.

On the other hand, an excessively great refractive power of the thirdlens group (L₃) violating the lower limit of condition (5) would make itdifficult to correct distortion and coma throughout the entire zoomrange. In contrast thereto, if the upper limit of condition (5) isviolated, the refractive power of the third lens group (L₃) would beexcessively decreased, which also reduces the refractive power of thefourth lens group (L₄) in relation with the above mentioned conditions(2) and (3). This is unfavorable to the telephoto-type desired in thelonger focal length side, which leads to a bulkiness of the lens system.

Condition (6) defines the focal length of the first lens group (L₁) soas to balance the optical performance of the lens system throughout theentire zoom range. If the lower limit of condition (6) is violated, itwould be difficult to correct spherical aberration and astigmatism inthe longer focal length side. Or, the total length of the whole lenssystem would be increased both at the shortest and longest focal lengthsif the upper limit of condition (6) is violated.

The following Tables 1 to 6 disclose, respectively, the first throughsixth embodiments of the present invention. In the Tables, f equals thefocal length, r is the radius of curvature with respective sub numbersindicating the surfaces from the object to image side along the opticalaxis, d represents the axial distance and includes both the air spacesand the actual thickness of the lens elements along the optical axis, Nequals the refractive index and again, the sub numbers refer to theparticular optical element from the object to image side, and finally, νequals the Abbe number and the sub numbers refer to the specific lenselements from the object to image side. The F-number and the variableair space distances in the Tables provided with three separate valuescorrespond to the values for the shortest, medium and longest focallengths, respectively.

                  TABLE 1                                                         ______________________________________                                         [Embodiment 1]                                                               f = 28.8 ˜ 50.0 ˜ 82.5 F.sub.No.  = 3.6 ˜ 4.0 ˜       4.63                                                                          Radius of    Axial    Refractive  Abbe                                        Curvature    Distance Index (N.sub.d)                                                                           Number (ν.sub.d)                         ______________________________________                                                  r.sub.1                                                                             333.333                                                                              d.sub.1                                                                           1.70 N.sub.1                                                                             1.7725                                                                              ν.sub.1                                                                         49.8                                   r.sub.2                                                                             37.379                                                                               d.sub.2                                                                           6.00                                                         r.sub.3                                                                             374.702                                                                              d.sub.3                                                                           5.00 N.sub.2                                                                             1.80741                                                                             ν.sub.2                                                                         31.6                                   r.sub.4                                                                             -68.960                                                       L.sub.1                d.sub.4                                                                           0.12                                                         r.sub.5                                                                             -175.441                                                                             d.sub.5                                                                           1.60 N.sub.3                                                                             1.7725                                                                              ν.sub.3                                                                         49.8                                   r.sub.6                                                                             35.419                                                                               d.sub.6                                                                           1.80                                                         r.sub.7                                                                             30.978                                                                               d.sub.7                                                                           2.70 N.sub.4                                                                             1.84666                                                                             ν.sub.4                                                                         23.9                                   r.sub.8                                                                             42.047                                                                   d.sub.8 41.48 ˜ 14.19 ˜  0.80                                    r.sub.9                                                                             36.673                                                                               d.sub.9                                                                           1.10 N.sub.5                                                                             1.834 ν.sub.5                                                                         37.1                                   r.sub.10                                                                            18.006                                                                               d.sub.10                                                                          7.80 N.sub.6                                                                             1.6968                                                                              ν.sub.6                                                                         56.5                                   r.sub.11                                                                            -35.528                                                       L.sub.2                d.sub.11                                                                          1.10 N.sub.7                                                                             1.75  ν.sub.7                                                                         25.1                                   r.sub.12                                                                            -104.959                                                                             d.sub.12                                                                          0.12                                                         r.sub.13                                                                            31.099                                                                               d.sub.13                                                                          2.60 N.sub.8                                                                             1.618 ν.sub.8                                                                         63.5                                   r.sub.14                                                                            88.117                                                                   d.sub.14  4.20 ˜ 11.57 ˜ 21.55                                   r.sub.15                                                                            -102.718                                                                             d.sub.15                                                                          2.20 N.sub.9                                                                             1.80518                                                                             ν.sub.9                                                                         25.4                         L.sub.3   r.sub.16                                                                            -26.126                                                                              d.sub.16                                                                          1.00 N.sub.10                                                                            1.7425                                                                              ν.sub.10                                                                        52.5                                   r.sub.17                                                                            37.626                                                                   d.sub.17 18.85 ˜ 11.49 ˜  1.50                                   r.sub.18                                                                            116.519                                                                              d.sub.18                                                                          5.00 N.sub.11                                                                            1.6405                                                                              ν.sub.11                                                                        60.1                                   r.sub.19                                                                            -31.574                                                                              d.sub.19                                                                          0.12                                                         r.sub.20                                                                            134.730                                                       L.sub.4                d.sub.20                                                                          3.2  N.sub.12                                                                            1.67  ν.sub.12                                                                        57.1                                   r.sub.21                                                                            -64.837                                                                              d.sub.21                                                                          2.0                                                          r.sub.22                                                                            -27.714                                                                              d.sub.22                                                                          1.40 N.sub.13                                                                            1.7569                                                                              ν.sub.13                                                                        31.8                                   r.sub.23                                                                            -831.721                                                      f.sub.1 = -41.667, f.sub.2 = 30.853, f.sub.3 = -39.370, f.sub.4 =             ______________________________________                                        56.840                                                                    

                  TABLE 2                                                         ______________________________________                                         [Embodiment 2]                                                               f = 28.8 ˜ 50.0 ˜ 82.5 F.sub.No. = 3.6 ˜ 4.0 ˜        4.63                                                                          Radius of    Axial    Refractive  Abbe                                        Curvature    Distance Index (N.sub.d)                                                                           Number (ν.sub.d)                         ______________________________________                                                  r.sub.1                                                                             250.000                                                                              d.sub.1                                                                           1.70 N.sub.1                                                                             1.6968                                                                              ν.sub.1                                                                         55.4                                   r.sub.2                                                                             33.933                                                                               d.sub.2                                                                           7.00                                                         r.sub.3                                                                             502.974                                                                              d.sub.3                                                                           5.50 N.sub.2                                                                             1.7106                                                                              ν.sub.2                                                                         43.3                                   r.sub.4                                                                             -59.941                                                       L.sub.1                d.sub.4                                                                           0.10                                                         r.sub.5                                                                             -93.188                                                                              d.sub.5                                                                           1.50 N.sub.3                                                                             1.6968                                                                              ν.sub.3                                                                         55.4                                   r.sub.6                                                                             39.682                                                                               d.sub.6                                                                           0.10                                                         r.sub.7                                                                             31.455                                                                               d.sub.7                                                                           3.30 N.sub.4                                                                             1.80518                                                                             ν.sub.4                                                                         25.4                                   r.sub.8                                                                             46.417                                                                   d.sub.8 46.00 ˜ 16.08 ˜ 1.20                                     r.sub.9                                                                             41.504                                                                               d.sub.9                                                                           1.00 N.sub.5                                                                             1.8075                                                                              ν.sub.5                                                                         35.5                                   r.sub.10                                                                            17.645                                                                               d.sub.10                                                                          7.00 N.sub.6                                                                             1.72  ν.sub.6                                                                         50.3                                   r.sub.11                                                                            -30.307                                                       L.sub.2                d.sub.11                                                                          1.50 N.sub.7                                                                             1.80518                                                                             ν.sub.7                                                                         25.4                                   r.sub.12                                                                            -88.826                                                                              d.sub.12                                                                          0.15                                                         r.sub.13                                                                            31.188                                                                               d.sub.13                                                                          3.00 N.sub.8                                                                             1.64  ν.sub.8                                                                         60.2                                   r.sub.14                                                                            120.353                                                                  d.sub.14 3.70 ˜ 9.33 ˜ 16.73                                     r.sub.15                                                                            -121.072                                                                             d.sub.15                                                                          3.50 N.sub.9                                                                             1.84666                                                                             ν.sub.9                                                                         23.9                                   r.sub.16                                                                            -21.648                                                                              d.sub.16                                                                          1.30 N.sub.10                                                                            1.7725                                                                              ν.sub.10                                                                        49.8                         L.sub.3   r.sub.17                                                                            30.431                                                                               d.sub.17                                                                          2.00                                                         r.sub.18                                                                            - 37.636                                                                             d.sub.18                                                                          1.00 N.sub.11                                                                            1.7725                                                                              ν.sub.11                                                                        49.8                                   r.sub.19                                                                            -59.214                                                                  d.sub.19 13.73 ˜ 8.10 ˜ 0.70                                     r.sub.20                                                                            -205.345                                                                             d.sub.20                                                                          2.50 N.sub.12                                                                            1.7725                                                                              ν.sub.12                                                                        49.8                                   r.sub.21                                                                            -34.240                                                                              d.sub.21                                                                          0.10                                                         r.sub.22                                                                            147.228                                                       L.sub.4                d.sub.22                                                                          1.30 N.sub.13                                                                            1.65446                                                                             ν.sub.13                                                                        33.9                                   r.sub.23                                                                            26.877                                                                               d.sub.23                                                                          10.00                                                                              N.sub.14                                                                            1.6583                                                                              ν.sub.14                                                                        58.5                                   r.sub.24                                                                            -18.696                                                                              d.sub.24                                                                          1.20 N.sub.15                                                                            1.805 ν.sub.15                                                                        41.0                                   r.sub.25                                                                            -118.697                                                      f.sub.1 =-45.455, f.sub.2 = 28.902, f.sub.3 = -27.051, f.sub.4                ______________________________________                                        = 44.352                                                                  

                  TABLE 3                                                         ______________________________________                                         [Embodiment 3]                                                               f = 28.8 ˜ 50.0 ˜ 82.5 F.sub.No. = 3.6 ˜ 4.0 ˜        4.63                                                                          Radius of     Axial    Refractive  Abbe                                       Curvature     Distance Index (N.sub.d)                                                                           Number (ν.sub.d)                        ______________________________________                                                  r.sub.1                                                                             69.842                                                                                d.sub.1                                                                           1.70 N.sub.1                                                                             1.7725                                                                              ν.sub.1                                                                         49.8                                  r.sub.2                                                                             30.030                                                                                d.sub.2                                                                           10.00                                                       r.sub.3                                                                             -3969.87                                                                              d.sub.3                                                                           5.40 N.sub.2                                                                             1.80741                                                                             ν.sub.2                                                                         31.6                                  r.sub.4                                                                             -67.672                                                       L.sub.1                 d.sub.4                                                                           0.12                                                        r.sub.5                                                                             -93.265                                                                               d.sub.5                                                                           1.60 N.sub.3                                                                             1.7725                                                                              ν.sub.3                                                                         49.8                                  r.sub.6                                                                             40.451                                                                                d.sub.6                                                                           1.80                                                        r.sub.7                                                                             33.126                                                                                d.sub.7                                                                           3.00 N.sub.4                                                                             1.84666                                                                             ν.sub.4                                                                         23.9                                  r.sub.8                                                                             46.216                                                                    d.sub.8 44.34 ˜  15.27 ˜ 0.80                                   r.sub.9                                                                             41.075                                                                                d.sub.9                                                                           1.10 N.sub.5                                                                             1.834 ν.sub.5                                                                         37.1                                  r.sub.10                                                                            18.877                                                                                d.sub.10                                                                          8.80 N.sub.6                                                                             1.6968                                                                              ν.sub.6                                                                         56.5                                  r.sub.11                                                                            -37.861                                                       L.sub.2                 d.sub.11                                                                          1.10 N.sub.7                                                                             1.75  ν.sub.7                                                                         25.1                                  r.sub.12                                                                            -97.066                                                                               d.sub.12                                                                          0.12                                                        r.sub.13                                                                            33.450                                                                                d.sub.13                                                                          2.70 N.sub.8                                                                             1.618 ν.sub.8                                                                         63.5                                  r.sub.14                                                                            151.381                                                                   d.sub.14  3.90 ˜ 11.01 ˜ 20.72                                  r.sub.15                                                                            -90.071                                                                               d.sub.15                                                                          2.20 N.sub.9                                                                             1.80518                                                                             ν.sub.9                                                                         25.4                        L.sub.3   r.sub.16                                                                            -25.171                                                                               d.sub.16                                                                          1.00 N.sub.10                                                                            1.7495                                                                              ν.sub.10                                                                        50.0                                  r.sub.17                                                                            39.435                                                                    d.sub.17 ˜  18.32 ˜ 11.21 ˜ 1.50                          r.sub.18                                                                            -2221.97                                                                              d.sub.18                                                                          4.50 N.sub.11                                                                            1.671 ν.sub.11                                                                        51.7                                  r.sub.19                                                                            -27.619                                                                               d.sub.19                                                                          0.12                                                        r.sub.20                                                                            188.554                                                       L.sub.4                 d.sub.20                                                                          3.20 N.sub.12                                                                            1.67  ν.sub.12                                                                        57.1                                  r.sub.21                                                                            -70.944                                                                               d.sub.21                                                                          2.30                                                        r.sub.22                                                                            -26.428                                                                               d.sub.22                                                                          1.40 N.sub.13                                                                            1.7552                                                                              ν.sub.13                                                                        27.5                                  r.sub.23                                                                            -133.035                                                      f.sub.1 = -41.667, f.sub.2 = 31.034, f.sub.3 = -38.478, f.sub.4 =             ______________________________________                                        59.847                                                                    

                  TABLE 4                                                         ______________________________________                                         [Embodiment 4]                                                               f = 28.8 ˜ 50.0 ˜ 82.5 F.sub.No. = 3.6 ˜ 4.0 ˜        4.6                                                                           Radius of    Axial    Refractive  Abbe                                        Curvature    Distance Index (N.sub.d)                                                                           Number (ν.sub.d)                         ______________________________________                                                  r.sub.1                                                                             ∞                                                                              d.sub.1                                                                           1.70 N.sub.1                                                                             1.7725                                                                              ν.sub.1                                                                         49.8                                   r.sub.2                                                                             46.512                                                                               d.sub.2                                                                           6.20                                                         r.sub.3                                                                             419.342                                                                              d.sub.3                                                                           6.22 N.sub.2                                                                             1.80741                                                                             ν.sub.2                                                                         31.6                                   r.sub.4                                                                             -74.038                                                       L.sub.1                d.sub.4                                                                           0.12                                                         r.sub.5                                                                             -216.486                                                                             d.sub.5                                                                           1.60 N.sub.3                                                                             1.7725                                                                              ν.sub.3                                                                         49.8                                   r.sub.6                                                                             33.619                                                                               d.sub.6                                                                           1.80                                                         r.sub.7                                                                             31.816                                                                               d.sub.7                                                                           3.00 N.sub.4                                                                             1.84666                                                                             ν.sub.4                                                                         23.9                                   r.sub.8                                                                             43.525                                                                   d.sub.8 42.42 ˜ 14.56 ˜ 0.80                                     r.sub.9                                                                             36.866                                                                               d.sub.9                                                                           1.10 N.sub.5                                                                             1.834 ν.sub.5                                                                         37.1                                   r.sub.10                                                                            18.475                                                                               d.sub.10                                                                          7.80 N.sub.6                                                                             1.6968                                                                              ν.sub.6                                                                         56.5                                   r.sub.11                                                                            -35.926                                                       L.sub.2                d.sub.11                                                                          1.10 N.sub.7                                                                             1.75  ν.sub.7                                                                         25.1                                   r.sub.12                                                                            -105.234                                                                             d.sub.12                                                                          0.12                                                         r.sub.13                                                                            30.137                                                                               d.sub.13                                                                          2.60 N.sub.8                                                                             1.618 ν.sub.8                                                                         63.5                                   r.sub.14                                                                            82.003                                                                   d.sub.14 4.20 ˜ 11.51 ˜ 21.48                                    r.sub.15                                                                            -110.161                                                                             d.sub.15                                                                          2.20 N.sub.9                                                                             1.80518                                                                             ν.sub.9                                                                         25.4                         L.sub.3   r.sub.16                                                                            -25.752                                                                              d.sub.16                                                                          1.00 N.sub.10                                                                            1.7495                                                                              ν.sub.10                                                                        50.0                                   r.sub.17                                                                            37.690                                                                   d.sub.17 18.78 ˜ 11.47 ˜ 1.50                                    r.sub.18                                                                            140.406                                                                              d.sub.18                                                                          4.80 N.sub.11                                                                            1.671 ν.sub.11                                                                        51.7                                   r.sub.19                                                                            -33.731                                                                              d.sub.19                                                                          0.12                                                         r.sub.20                                                                            198.465                                                       L.sub.4                d.sub.20                                                                          3.20 N.sub.12                                                                            1.67  ν.sub.12                                                                        57.1                                   r.sub.21                                                                            -73.957                                                                              d.sub.21                                                                          2.31                                                         r.sub.22                                                                            -27.272                                                                              d.sub.22                                                                          1.40 N.sub.13                                                                            1.7552                                                                              ν.sub.13                                                                        27.5                                   r.sub.23                                                                            -147.561                                                      f.sub.1 = -41.667, f.sub.2 = 30.660, f.sub.3 = -39.606, f.sub.4 =             ______________________________________                                        58.908                                                                    

                  TABLE 5                                                         ______________________________________                                         [Embodiment 5]                                                               f = 28.8 ˜ 50.0 ˜ 82.5 F.sub.No. = 3.6 ˜ 4.0 ˜        4.6                                                                           Radius of    Axial    Refractive  Abbe                                        Curvature    Distance Index (N.sub.d)                                                                           Number (ν.sub.d)                         ______________________________________                                                  r.sub.1                                                                             206.742                                                                              d.sub.1                                                                           1.70 N.sub.1                                                                             1.7725                                                                              ν.sub.1                                                                         49.8                                   r.sub.2                                                                             34.144                                                                               d.sub.2                                                                           7.50                                                         r.sub.3                                                                             -2634.98                                                                             d.sub.3                                                                           5.40 N.sub.2                                                                             1.80741                                                                             ν.sub.2                                                                         31.6                                   r.sub.4                                                                             -59.791                                                       L.sub.1                d.sub.4                                                                           0.12                                                         r.sub.5                                                                             -130.332                                                                             d.sub.5                                                                           1.60 N.sub.3                                                                             1.7725                                                                              ν.sub.3                                                                         49.8                                   r.sub.6                                                                             32.411                                                                               d.sub.6                                                                           1.80                                                         r.sub.7                                                                             29.257                                                                               d.sub.7                                                                           3.00 N.sub.4                                                                             1.84666                                                                             ν.sub.4                                                                         23.9                                   r.sub.8                                                                             38.534                                                                   d.sub.8 30.69 ˜ 10.42 ˜ 0.80                                     r.sub.9                                                                             34.366                                                                               d.sub.9                                                                           1.10 N.sub.5                                                                             1.834 ν.sub.5                                                                         37.1                                   r.sub.10                                                                            17.178                                                                               d.sub.10                                                                          9.00 N.sub.6                                                                             1.6968                                                                              ν.sub.6                                                                         56.5                                   r.sub.11                                                                            -36.473                                                       L.sub.2                d.sub.11                                                                          1.10 N.sub.7                                                                             1.75  ν.sub.7                                                                         25.1                                   r.sub.12                                                                            -80.970                                                                              d.sub.12                                                                          0.12                                                         r.sub.13                                                                            30.964                                                                               d.sub.13                                                                          2.6  N.sub.8                                                                             1.618 ν.sub.8                                                                         63.5                                   r.sub.14                                                                            83.804                                                                   d.sub.14 3.9 ˜ 12.29 ˜ 23.19                                     r.sub.15                                                                            -87.500                                                                              d.sub.15                                                                          2.20 N.sub.9                                                                             1.80518                                                                             ν.sub.9                                                                         25.4                         L.sub.3   r.sub.16                                                                            -25.041                                                                              d.sub.16                                                                          1.00 N.sub.10                                                                            1.7495                                                                              ν.sub.10                                                                        50.0                                   r.sub.17                                                                            37.609                                                                   d.sub.17 20.79 ˜ 12.40 ˜  1.50                                   r.sub.18                                                                            126.975                                                                              d.sub.18                                                                          4.80 N.sub.11                                                                            1.61762                                                                             ν.sub.11                                                                        52.7                                   r.sub.19                                                                            -32.310                                                                              d.sub.19                                                                          0.12                                                         r.sub.20                                                                            131.990                                                       L.sub.4                d.sub.20                                                                          3.20 N.sub.12                                                                            1.58913                                                                             ν.sub.12                                                                        61.1                                   r.sub.21                                                                            -68.060                                                                              d.sub.21                                                                          2.35                                                         r.sub.22                                                                            -28.435                                                                              d.sub.22                                                                          1.40 N.sub.13                                                                            1.80518                                                                             ν.sub.13                                                                        25.4                                   r.sub.23                                                                            -103.243                                                      f.sub.1 = -33.333, f.sub.2 = 28.604, f.sub.3 = -36.785, f.sub.4 =             ______________________________________                                        53.285                                                                    

                  TABLE 6                                                         ______________________________________                                         [Embodiment 6]                                                               f = 28.8 ˜ 55.0 ˜ 102.0 F.sub.No. = 3.6 ˜ 4.0 ˜       4.6                                                                           Radius of    Axial    Refractive  Abbe                                        Curvature    Distance Index       Number                                      ______________________________________                                                  r.sub.1                                                                             87.172                                                                               d.sub.1                                                                           2.20 N.sub.1                                                                             1.7725                                                                              ν.sub.1                                                                         49.8                                   r.sub.2                                                                             31.737                                                                               d.sub.2                                                                           13.50                                                        r.sub.3                                                                             -97.886                                                                              d.sub.3                                                                           4.50 N.sub.2                                                                             1.8075                                                                              ν.sub.2                                                                         35.5                         L.sub.1   r.sub.4                                                                             -53.394                                                                              d.sub.4                                                                           0.12                                                         r.sub.5                                                                             -93.887                                                                              d.sub.5                                                                           2.0  N.sub.3                                                                             1.5168                                                                              ν.sub.3                                                                         64.1                                   r.sub.6                                                                             22.883                                                                               d.sub.6                                                                           6.5  N.sub.4                                                                             1.84666                                                                             ν.sub.4                                                                         23.9                                   r.sub.7                                                                             34.221                                                                   d.sub.7 29.49 ˜ 9.91 ˜ 0.80                                      r.sub.8                                                                             31.408                                                                               d.sub.8                                                                           1.50 N.sub.5                                                                             1.84666                                                                             ν.sub.5                                                                         23.9                                   r.sub.9                                                                             19.904                                                                               d.sub.9                                                                           11.00                                                                              N.sub.6                                                                             1.58913                                                                             ν.sub.6                                                                         61.1                                   r.sub.10                                                                            -46.380                                                       L.sub.2                d.sub.10                                                                          1.50 N.sub.7                                                                             1.84666                                                                             ν.sub.7                                                                         23.9                                   r.sub.11                                                                            -87.558                                                                              d.sub.11                                                                          0.12                                                         r.sub.12                                                                            37.710                                                                               d.sub.12                                                                          3.60 N.sub.8                                                                             1.618 ν.sub.8                                                                         63.5                                   r.sub.13                                                                            111.660                                                                  d.sub.13 3.40 ˜ 18.28 ˜ 40.44                                    r.sub.14                                                                            -125.384                                                                             d.sub.14                                                                          3.50 N.sub.9                                                                             1.80518                                                                             ν.sub.9                                                                         25.4                                   r.sub.15                                                                            -26.547                                                                              d.sub.15                                                                          1.10 N.sub.10                                                                            1.7495                                                                              ν.sub.10                                                                        50.0                         L.sub.3   r.sub.16                                                                            286.185                                                                              d.sub.16                                                                          1.50                                                         r.sub.17                                                                            -49.005                                                                              d.sub.17                                                                          1.10 N.sub.11                                                                            1.7725                                                                              ν.sub.11                                                                        49.8                                   r.sub.18                                                                            84.645                                                                   d.sub.18  19.00 ˜ 10.20 ˜ 1.00                                   r.sub.19                                                                            -2177.90                                                                             d.sub.19                                                                          4.00 N.sub.12                                                                            1.5168                                                                              ν.sub.12                                                                        64.1                                   r.sub.20                                                                            -33.967                                                                              d.sub.20                                                                          0.12                                               L.sub.4   r.sub.21                                                                            62.142                                                                               d.sub.21                                                                          7.00 N.sub.13                                                                            1.5168                                                                              ν.sub.13                                                                        64.1                                   r.sub.22                                                                            -25.886                                                                              d.sub.22                                                                          1.40 N.sub.14                                                                            1.85026                                                                             ν.sub.14                                                                        32.3                                   r.sub.23                                                                            -52.697                                                       f.sub.1 = -40.000, f.sub.2 = 36.131, f.sub.3 = -30.661, f.sub.4 =             ______________________________________                                        38.389                                                                    

In the embodiments, it should be noted that the first lens group (L₁)includes at least two positive lens elements on the image side of thefront negative lens. Further, it is recommendable that the first lensgroup (L₁) further includes at least one negative lens element betweenthe two positive lens elements as in the embodiments. The image side oneof the two positive lens elements may be cemented to the negative lenselement as in the sixth embodiment.

Further, in the embodiments, the second lens group (L₂) includes anobject side positive lens consisting of a biconvex lens elements and apair of negative meniscus lens elements with different refractive indexand Abbe number cemented on both sides of the biconvex lens element,respectively, and an image side positive single lens element. Thisconstruction is effective to correct aberrations of the second lensgroup (L₂) by itself, which is favorable to correct spherical aberrationand chromatic aberration throughout the entire zoom range. Such aconstruction for the second lens group (L₂) is also advantageous incomparison with a second lens group composed of the same number of lenselements consisting of two doublets in view of the reduced axial lengthof the second lens group (L₂) and the illumination for the marginal areaof the image. However, the second lens group (L₂) can be alternativelyconstructed by an object side doublet and an image side singlet with thenumber of necessary lens elements for the second lens group reduced byone, and such a construction is generally within the scope of thepresent invention. In this alternative construction of the second lensgroup (L₂), the relatively insufficient aberration correction within thesecond lens group (L₂) should be corrected by means of the change in thesecond variable air space (l₂) between the second and third lens groups(L₂ and L₃).

In the first and third to fifth embodiments, the fourth lens groupincludes two positive lens elements and a negative lens element, whereinan air space of a positive meniscus shape convex to the image side isformed between the image side one of the two positive lens elements andthe negative lens element. Such a fourth lens group is favorable to thecorrection of the lateral aberration in the shorter focal length side,and makes it possible to secure the necessary illumination for themarginal area of the image with a limited diameter of the fourth lensgroup.

With respect to the lens movements, the second lens group (L₂) and thefourth lens group (L₄) are cooperatively moved in the same speed in thefirst to fifth embodiments, while the movements in all of the threemovable lens groups are each independent in the sixth embodiment.

As can be readily appreciated, it is possible to deviate from the aboveembodiments of the present invention and, as will be readily understoodby those skilled in the optical art, the invention is capable of manymodifications and improvements within the scope and spirit thereof.Accordingly, it will be understood that the invention is not to belimited by these specific embodiments, but only by the scope and spiritof the appended claims.

What is claimed is:
 1. A zoom lens system comprising:a first lens groupof a negative refractive power, said first lens group including anegative lens as the first lens at the object side end of the first lensgroup; a second lens group of a positive refractive power located on theimage side of the first lens group with a first variable air spacebetween the first and second lens groups, said second lens groupincluding a pair of positive lenses, the object side one of the pair ofpositive lenses consisting of a biconvex lens element and a pair ofnegative meniscus lens elements, respectively, cemented on both sides ofthe biconvex lens element, and the image side one of the pair ofpositive lenses being a single lens element; a third lens group of anegative refractive power located on the image side of the second lensgroup with a second variable air space between the second and third lensgroups, and a fourth lens group of a positive refractive power locatedon the image side of the third lens group with a third variable spacebetween the third and fourth lens groups, wherein the first and thirdvariable air spaces are reduced and the second variable air space isincreased in accordance with the increase of the focal length of thewhole lens system during the zooming operation.
 2. A zoom lens systemcomprising:a first lens group of a negative refractive power; a secondlens group of a positive refractive power located on the image side ofthe first lens group with a first variable air space between the firstand second lens groups, said second lens group including a pair ofpositive lenses, the object side one of the pair of positive lensesconsisting of a biconvex lens element and a pair of negative meniscuslens elements, respectively, cemented on both sides of the biconvex lenselement, and the image side one of the pair of positive lenses being asingle lens element; a third lens group of a negative refractive powerlocated on the image side of the second lens group with a secondvariable air space between the second and third lens groups, and afourth lens group of a positive refractive power located on the imageside of the third lens group with a third variable air space between thethird and fourth lens group, said fourth lens group including at leasttow positive lens elements, a negative lens element and an air space ofa positive meniscus shape convex to the image side formed between theimage side one of the two positive lens elements and the negative lenselement, wherein the first and third variable air spaces are reduced andthe second variable air space is increased in accordance with theincrease of the focal length of the whole lens system during the zoomingoperation.
 3. The invention of claim 2, wherein the first lens groupincludes a negative lens as the first lens on the object side end of thefirst lens group.
 4. The invention of claim 3, wherein the first lensgroup further includes at least two positive lens elements on the imageside of the negative lens, and one negative lens element between the twopositive lens elements.